This project seeks an understanding of cerebellar function both at the level of its organ role within a larger system and at the level of circuitry. In the latter case one asks how the organ role is accomplished by the interconnected neurons of the cerebellum. At present the major focus is on the cerebellum and cerebellum-like structures of weakly electric mormyrid fish. These structures offer numerous advantages, both physiological and anatomical, for an analysis of cerebellar function. In addition the electro-location and communication functions which these structures mediate are accessible to a detailed and quantitative behavioral analysis. While the emphasis of this project is on the CNS, some behavioral studies have been and are being done. Some of the circuitry questions are also being worked on in an electro-anatomical study of the relationships between cerebellar cortex and cerebellar nucleus in the South American alligator. This animal offers the advantages of a flat cortex and well developed deep nuclei. Finally, postural control studies are being pursued in higher vertebrates as part of an approach to the organ function of the cerebellum in these animals.